Tuesday, December 3, 2013

New paper finds severe drought is more common during cold periods, droughts driven by solar activity

A new paper under open review for Climate of the Past finds severe droughts in Eastern China were much more common during the Little Ice Age than during the current warm period, and that no severe droughts occurred in E. China during the past 357 years from 1642-1999. Data from the paper demonstrates there is nothing unusual, unprecedented, or unnatural regarding 20th century drought in Eastern China. The authors also find solar activity was the primary driver of most of the severe droughts over the past millennium. The paper adds to many other peer-reviewed publications finding droughts and other extreme weather are more common during cold periods in comparison to warm periods, i.e. a warmer climate is a more benign climate.

Reconstructed droughts shown in first column, computer modelled droughts shown in second column

There have been no severe droughts since 1642 and current precipitation levels [year 2000] are only slightly below the mean of the past millennium.There is nothing unusual, unprecedented, or unnatural regarding current drought.

Y. Peng1, C. Shen2, H. Cheng3,4, and Y. Xu51Department of Earth Environmental Science, Xi'an Jiaotong University, Xi'an, China2Key Laboratory of Plateau Lake Ecology and Global Change, Yunnan Normal University, Kunming, China3Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an, China4Department of Geology and Geophysics, University of Minnesota, Minneapolis, USA5Laboratory for Climate Studies, China Meteorological Administration, Beijing, ChinaAbstract. We use proxy data and modeled data from 1000 yr model simulations with a variety of climate forcings to examine the occurrence of severe events of persistent drought over eastern China during the last millennium and to diagnose the mechanisms. Results show that the model was able to simulate many aspects of the low-frequency (periods greater than 10 yr) variations of precipitation over eastern China during the last millennium, including most of the severe persistent droughts such as those in the 1130s, 1200s, 1350s, 1430s, 1480s, and the late 1630s–mid-1640s. These six droughts are identified both in the proxy data and in the modeled data and are consistent with each other in terms of drought intensity, duration, and spatial coverage.

Our analyses suggest that monsoon circulation can lock into a drought-prone mode that may last for years to decades and supports the suggestion that generally reduced monsoon in eastern Asia were associated with the land–sea thermal contrast. Study on the wavelet transform and spectral analysis reveals six well-captured events occurred all at the drought stages of statistically significant 15–35 yr timescale. A modeled data intercomparison suggests that solar activity is the primary driver in the occurrence of the 1130s, 1350s, 1480s, and late 1630s–mid-1640s droughts. Although the El-Niño–Southern Oscillation (ENSO) plays an important role in monsoon variability, a temporally consistent relationship between the droughts and SST pattern in the Pacific Ocean could not be found in the model. Our analyses also indicate that large volcanic eruptions play a role as an amplifier in the drought of 1635–1645 and caused the model to overestimate the decreasing trends in summer precipitation over eastern China during the mid-1830s and the mid-1960s.